Method of refining mineral oils



atented May 14, 1929.

PATENT OFFICE.

,an'rnun recurrent, or BERKELEY, cnnrronnra, ASSIGNOR T0 nrcnnrnrin on. comrnnr or CALIFORNIA, or SAN rnanorsco, CALIFORNIA, A conronnrrcn or DEL- AWARE.

' mnrnon on imrmrne mmnnar. OILS.

lto Drawing.-

t scribed in this application is applicable to all mineral oils such as lubricating oils, kerosene,

gasoline, shale oils, etc. For the purpose of.

simplifying the description, reference will be made to lubricating oils-only. 4

llrude lubricating oil, as'obtained during the fractional distillation of petroleum (and after removing its possible content of solid para by freezing) is a mixture of saturated and unsaturated hydrocarbons, together with it asphaltic materials, resins, organic acids, sulphur compounds, nitrogen bases, and other substances of an undefined nature. These latter substances are readily oxidized by atmospheric oxygen at ordinary or moderately an elevated temperatures and. are responsible for the color changes which take place when refined oils are stored. These oxidizable substances are removed with diificulty when oil is refined by the methods now in common use. It is customary, in refinery practice, to speak of lubricating oils as more or less stable in inverse proportion to their darkening by atmospheric oxidation. Oils of higher stability darken more slowly, etc. The term stability as used in the present description 0t my invention is employed in this technical sense.

In order to show the nature of my invention, it is desirable to describe the methods now in common use in oil refineries. Crude lubricating oil is treated with varying amounts, from 2% to by weight, of

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sulphuric acid, which, according to the nature of the oil, is either 66 degree acid, or fuming acid, or a mixture or combination of both terms of this acid. This treatment removes the ingredients named above, with the exception of those which affect the stability of the oilg but it also removes, to a marked extent, the unsaturated hydrocarbons upon which the lubricating qualities of the oil in'large degree depend. It is, therefore, necessary to restrict the quantity of sulphuric acid to a minimum to avoid heavy losses of valuable hydrocarbons; and such restriction may result in only partial removal of some of the impurities named.

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'(as much as 15% by weight).

. Application filed May 18, 1926. Serial-No. 109,970.

After treatment with sulphuric acid, the oil is washed with an alkali, to remove the organic'as well as the mineral acids present. Oils so treated are sometimes pale, but usually are dark, and they are quite unstable towards air. Their color, and to some extent their stability, is thereupon improved by treating the washed oil with charcoal, or more customarily in the United States with a type of clay known as tullers earth. Considerable proportions of clay are sometimes required The removal of the clay from the treated oil, and the recovery of the oil remaining in it, and the regeneration of the clay for repeated use, are troublesome and expensive operations.

My invention consists in the discovery that a part, or all, of the sulphuric acid normally used in refining lubricating oils, may be re placed with phosphoric acid, and that oils treated with phosphoric acid, or with a mix ture of phosphoric and sulphuric acids,- or with sulphuric acid followed by phosphoric acid, may have any desired color and are of much greater stability towards atmospheric oirygen than oils which have been treated with c ay.

It is, of course, necessary to remove the excess of phosphoric acid which may have dissolved in the oil by washing with alkalies, and it may be desirable to remove any sulphuric acid.

In fact, since crude lubricating oils are undefinable mixtures, and vary from locality to locality, it is impossible to give a single definite formula for the use of phosphoric a iclild which shall be applicable to all oils. amount of this acid which may be required, the amount of sulphuric acid which should be used in combination with it,the duration of the treatment with each acid,1or with both, and the temperature at which these several treatments may be best carried on, and the extent to which intermediate washing for the removal of a part of the acids employed should be practised, must vary within wide limits to obtain the desired results with varying oils.

Before giving examples of the actual proportions which I have employed in given cases, it is necessary to glvesome description of the method whereby stabilities of oils may be compared. For such purpose, I place four fluid ounces of-oil in an eight ounce Erlenmeyer flask, which is thereupon heated, without any stopper, in an oven maintained at 95 centigrade, through which air is freely circulating. The-heating is continued for six hours. After this time, the heated oil is compared with the original oil in a colorimeter, and the relative depths of heated and unheated oil are noted when the two oils match in color intensity. The results are then expressed in percentage of increase of color, of the heated oil over the original sample. Four samples of clay treated oils, 'purchased from four different refiners, were examined in this manner and were found to give the following results (after six hours heating as described Oil A darkened 25%; oil B, 110%; oil C, 22% and oil D, 47%.

As examples of the manner in which I employ phosphoric acid in refining and stabilizing lubricating oils, the following may be given:

(1) One hundred parts by weight of crude lubricating oil were treated with four (4).

parts by weight of 66 sulphuric acid. The temperature was 45 centigrade. After standing overnight, the oil was decanted from the heavy acid sludge, and heated with three (3) parts by weight of phosphoric acid (85%' strength). The temperature was 170 centigrade; and the time of heating was two hours. The mixture was mechanically stirred and air was excluded during this period by covering the vessel and conducting a current of oxygen-free gas through it. After spontaneous cooling during two hours, the oil was again decanted from the sludge which had formed, and washed with dilute sodium hydroxide and finally with water. The oil was next dehydrated by a current of warm, oxygen-free gas, and filtered through a piece of paper. This oil showed an increase of color, during six hours of heating as described of 8%. It was, therefore, of much higher stability than the oils which had been clay treated.

(2) One hundred (100) parts of crude. oil stock, of different origin, was treated with eight (8) parts of 66 sulphuric acid at 50 centigrade. After settling over night, the oil was decanted and washed with dilute sodium hydroxide and water. It was next heated with four (4) parts by weight of 85% phosphoric acid, as described above, with the exclusion of air, etc.; but the time of heatingwas three hours, and the temperature was 185 centigrade. After cooling and decanting the oil from the acid sludge,,it was neutralized by directly heating it, with mechanical stirring, with solid calcium hydrate, to 120 centrigrade, with exclusion of air.

-Upon cooling, the oil was filtered through paper. This oil, when heated to test its stap This oil now showed a marked increase in stability. It darkened only 5% in six hours. In addition to the very definite effect which phosphoric acid has on the stability of lubricating oils, it should be noted that it has a much more selective action on impurities than sulphuric acid, and that it has but slight action on the unsaturated hydrocarbons which are so important in the usefulness of the oil, and which sulphuric acid removes to so great an extent. It will, therefore be possible, as a rule, to use much less sulphuric acid in the refining of oil, when it is followed by phosphoric acid; the latter will remove impurities, but will not remove more than a very small proportion of the true lubricating hydrocarbons. The use of phosphoric acid thus results in a saving of oil values, as the sludge losses are very small.

The sludge obtained from the use of phosphoric acid contains practically all that had been added to the oil. The amount that goes into solution in theoil is very small. It is, therefore, possible to recover practically all the acid from the sludge for re-use. For this purpose, the sludge may be extracted by hot water, and the solution thus formed calcined to destroy the organic matter it contains.

Having thus described my invention, what 1 claim and desire to secure by Letters Patent 1s- 1. A method of refining crude mineral oil, which comprises first treating the oil with sulphuric acid at a temperature above but approaching atmospheric temperature and decanting the oil from the acid sludge, secondly, treating the oil to a higher temperature, treating the oil with phosphoric acid and again decanting the oil to remove the acid sludge, and, third, neutralizing any rev'maining acid content and removing the neutralizing agent.

2. A method'of refining crude mineral oil,

which comprises first treating the oil with 3. A method of refining crude mineral oil, to a higher temperature and treating the oil which comprises first treating the oil with with phosphoric acid and again decanting I sulphuric acid at a temperature above but apthe oil to remove the acid sludge, and, fourth, 10 preaching atmospheric temperature and deneutralizing any remaining acid content by canting the oil from the acid sludge, second, adding solid calcium hydrate and removing neutralizing the remaining acid content by the suspended solids by filtration. Washing with an alkali, third, heating the oil ARTHUR LACHMAN, 

